It is often necessary to withdraw one atmosphere from a package during the packaging process and to substitute a different atmosphere. For example, in modified atmosphere packaging, normal ambient oxygen may be withdrawn by a connection to an appropriate vacuum source and a desired atmosphere, for example composed of inert gases, may be substituted.
One application for this technology is in connection with packaging meats to extend their packaged life. A meat butchered in one location can be packaged in a relatively inert atmosphere so that its useful life is significantly extended. At a later time, the meat could be exposed to oxygen and thereby caused to "bloom" or turn red in color.
In many other applications, it is desirable to package a food product or other item in a specialized atmosphere. To accomplish this, manifolds are used which are capable of connecting the interior of the package selectively to a source of the desired gas or vacuum to withdraw existing gas from the package.
Generally, one or more trays are seated on the manifold, situated within an appropriate enclosure. At the appropriate times, gas is supplied or withdrawn from the tray. To obtain rapid gas exchange, a plurality of apertures are used around the trays to communicate the gas or vacuum source.
Because of the inherent complexity involved in separately supplying two different gaseous conditions to the same package while it is in the same position, these manifolds tend to be structurally complex. The resulting elaborate shapes necessary to supply separately both gas and vacuum communication, result in difficulties in cleaning these devices. As a result, sanitary conditions are difficult to maintain. The desired degree of cleanliness may not be maintained, or if maintained, is achieved at considerable cost both in terms of the cost of cleaning the materials and in downtime of the equipment.
Existing manifolds for these applications use a number of pieces. A block of material is "hogged-out" to form a depression in which the other pieces are inserted. Metal tubes are provided to provide communication with the package through the various plates inserted into the "hogged-out" block. Not only is this "hogged-out" block of metal expensive to manufacture, it tends to be limited in its application to a specific package configuration. Thus, a variety of such blocks may be required. Moreover, the use of tubular passages tends to cause difficulties in assembly and are likely sources for trapping bacteria and dirt. These structures also tend to have a lot of dead space which must be filled with the gas being supplied, increasing the time necessary for gas exchange.
Ideally, a manifold would quickly supply the desired gas under conditions of extreme cleanliness. Moreover, the ideal structure would be readily and easily cleaned. Finally, the ideal structure would have a minimum number of parts, and complex machining operations would be avoided.